Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (105,797)	$ (395,657)	$ (586,769)
Unrealized holding gains (losses), net	150,187	(51,834)	134,923
Foreign currency translation adjustment	(4,039)	546	809
Unrealized losses on cash flow hedges	(165)
Unrealized losses on cash flow hedges	65
Unrealized losses on cash flow hedges	(100)
Current year benefit plans gains (losses)	(347,993)	260,452	(29,823)
Total other comprehensive income (loss) before reclassifications	(202,010)	209,164	105,909
OTTI charges recognized in net income		9,800	47,822
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	3,374	4,287	6,190
Losses (gains) realized in net income		33,088	(9)
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	7		(178)
Amortization of prior service credit	(7,911)	(7,915)	(6,538)
Amortization of actuarial losses	14,494	41,436	37,916
Total reclassifications	9,964	80,696	85,203
Total gain (loss) during the period	(192,046)	289,860	191,112
Beginning balance	41,638	155,393	230,328
Ending balance	(297,843)	(105,797)	(395,657)
Unrealized holding gains (losses), net	(58,962)	20,311	(52,905)
Foreign currency translation adjustment	1,432	(165)	(290)
Current year benefit plans gains (losses)	136,587	(102,227)	11,705
Total other comprehensive income (loss) before reclassifications	79,122	(82,081)	(41,490)
OTTI charges recognized in net income		(3,847)	(18,770)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	(1,324)	(1,683)	(2,430)
Losses (gains) realized in net income		(12,987)	4
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	(3)		66
Amortization of prior service credit	3,105	3,107	2,566
Amortization of actuarial losses	(5,689)	(16,264)	(14,881)
Total reclassifications	(3,911)	(31,674)	(33,445)
Total gain (loss) during the period	75,211	(113,755)	(74,935)
Beginning balance	(64,159)	(240,264)	(356,441)
Ending balance	116,849	41,638	155,393
Unrealized holding gains (losses), net	91,225	(31,523)	82,018
Foreign currency translation adjustment	(2,607)	381	519
Current year benefit plans gains (losses)	(211,406)	158,225	(18,118)
Total other comprehensive income (loss) before reclassifications	(122,888)	127,083	64,419
OTTI charges recognized in net income		5,953	29,052
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	2,050	2,604	3,760
Losses (gains) realized in net income		20,101	(5)
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	4		(112)
Amortization of prior service credit	(4,806)	(4,808)	(3,972)
Amortization of actuarial losses	8,805	25,172	23,035
Total reclassifications	6,053	49,022	51,758
Total gain (loss) during the period	(116,835)	176,105	116,177
Ending balance	(180,994)	(64,159)	(240,264)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	115	(431)	(1,062)
Foreign currency translation adjustment	(4,039)	546	809
Unrealized losses on cash flow hedges	(165)
Total other comprehensive income (loss) before reclassifications	(4,204)	546	809
Amortization (Accretion) of gains (losses) on terminated cash flow hedges	7		(178)
Total reclassifications	7		(178)
Total gain (loss) during the period	(4,197)	546	631
Ending balance	(4,082)	115	(431)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	37,255	(91,835)	(138,319)
Unrealized holding gains (losses), net	(29,818)	77,794	(2,998)
Total other comprehensive income (loss) before reclassifications	(29,818)	77,794	(2,998)
OTTI charges recognized in net income		9,800	47,822
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	1	279	1,660
Losses (gains) realized in net income		41,217
Total reclassifications	1	51,296	49,482
Total gain (loss) during the period	(29,817)	129,090	46,484
Ending balance	7,438	37,255	(91,835)
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	18,450	152,199	9,757
Unrealized holding gains (losses), net	180,005	(129,628)	137,921
Total other comprehensive income (loss) before reclassifications	180,005	(129,628)	137,921
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	3,373	4,008	4,530
Losses (gains) realized in net income		(8,129)	(9)
Total reclassifications	3,373	(4,121)	4,521
Total gain (loss) during the period	183,378	(133,749)	142,442
Ending balance	201,828	18,450	152,199
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(161,617)	(455,590)	(457,145)
Current year benefit plans gains (losses)	(347,993)	260,452	(29,823)
Total other comprehensive income (loss) before reclassifications	(347,993)	260,452	(29,823)
Amortization of prior service credit	(7,911)	(7,915)	(6,538)
Amortization of actuarial losses	14,494	41,436	37,916
Total reclassifications	6,583	33,521	31,378
Total gain (loss) during the period	(341,410)	293,973	1,555
Ending balance	(503,027)	(161,617)	(455,590)
Beginning balance	(98,182)	(276,771)	(277,716)
Total gain (loss) during the period	(207,407)	178,589	945
Ending balance	$ (305,589)	$ (98,182)	$ (276,771)